Does Gabapentin actually work?

Hi everyone! So my 7 year old chihuahua mix has spontaneous separation anxiety regression. Usually triggered by a move or boarding. Normally within a few weeks we can get him back in shape, but this time is different and I’m not sure why. We did everything we usually do. Peanut butter kong, tvs on his favorite show, and he’s been on reconcile for years. We leave without saying anything or making a fuss, and he goes on at least 2 long walks each day.

For reason since we boarded him for Christmas none of this is working. We got him on gabapentin. Got him a crate as an additional safe space. Gave him a lick mat and a chew toy. We even bought an adaptdil collar for pheromones.

He just panics when we leave and howls. Our neighbors have complained and we’re moving out to avoid conflict. We chose to rent a stand alone house because we thought that might help, but I am loosing hope. I feel like I’ve tried everything the vet gave me and the meds aren’t working at all. Any advice? Thanks in advance!